Extreme Lifting With Mega Cranes for the Olmsted Dam

How engineers are using two massive cranes and creative construction methods to build one of the country's most ambitious—and important—infrastructure projects.

The Olmsted Locks and Dam is one of the biggest civil works jobs ever undertaken by the Army Corps of Engineers. Started in 1993 and set to be complete by 2016, the $2 billion program is about to enter a tough phase–constructing and hauling 36 12,000-square-foot concrete shells weighing about 3500 tons—yes, tons, not pounds—from the shore to the river bottom. It requires not just one, but two record-breakingly enormous mega cranes. One is the largest crane in North America. The other is the largest floating crane in the world.

Dams on the Ohio River

Until the Olmsted Locks and Dam project is complete, this stretch of the Ohio River on the Illinois–Kentucky border has to rely on two 81-year-old locks and rickety wooden wicket dams named Dam 52 and Dam 53. (The life of a lock and dam is 50 to 75 years.) Two temporary locks, with a design life of 20 years, were built in the 60s and 70s to supplement the old locks; 40 years later, they're still standing. And they're in very bad shape. If the locks were to fail, boats that haul around 90 million tons of rock, coal and other raw goods every year would not be able to get through because the river's height fluctuates as much as 50 feet over the course of a year.

This is the last dam to be replaced in a congressional project started in the 1950s to upgrade a series of turn-of-the-century dams along the Ohio River. Trawling freight along a river is much cheaper and carbon-footprint-friendly than driving it with a truck or riding it along a railroad. "One barge can tow the equivalent of about 890 trucks on the roadway," says Bill Gilmour, the Corps resident engineer for the project.

How the Wicket Dam and Locks Work

The wooden wickets on the old dams are large planks that are manually raised to a steep angle or lowered flat to control the river flow. Workers head out on the river on a steam-powered barge and use a long hook to raise and lower the wickets as needed. When raised, they block water and feed it to adjacent boat locks that harbor barges safely to a lower elevation when the river is low.

The locks are 1200-foot-long, 110-foot-wide enclosures with watertight doors. A boat coming down the river enters the lock chamber from the upper level. The doors are closed behind it, and the chamber is emptied of water through valves until the water level matches the lower part of the river. The boat can then safely pass to that part of the river.

When the wickets are down, boats bypass the locks altogether and go straight over them, which is possible about 58 percent of the year, when the river is high.

Pick 'Em Up, Haul 'Em Out, and Set 'Em Down: In-the-Wet Construction

The new dam will also have wickets, but they will be made of steel, with concrete foundations. Normally, dam builders would dry out part of the river with temporary cofferdams to pour that concrete. But for this project, they opted for in-the-wet construction, which requires mega-size cranes to lift and lay down the 3500-ton shells. "I'm not aware of any other projects in the world where people are lifting 3500-ton pieces of concrete," Gilmour says. "It's not normal."

On Aug. 21, the first concrete shell was successfully installed. The entire progression of lifting the shell and getting it on the river bottom takes about three weeks. After a shell is built in one of six riverside build yards—which alone can take 10 months—a gigantic crane on wheels, the super gantry crane, which could fit a 10-story building underneath itself, picks up the completed shell. Though the shells are heavy by normal standards, they're actually very thin and fragile; a special steel frame was designed that allows the crane to lift the shells without breaking them.

After the shell is lifted, workers take the super gantry crane and its cargo to the edge of the shore, where the shell is passed to the largest floating crane in the world, the catamaran barge. The catamaran barge guides the submerged shell with extreme precision to its final resting place at the bottom of the river, 30 feet below the surface. While the crane and the barge must place their loads to within inches, the basic concept of the operation is pretty simple.

"Pick 'em up, haul 'em out and set 'em down," Gilmour says, "like Legos." A project of this scale has never attempted in-the-wet, but Gilmour believes the process is more environmentally friendly, economical and time-efficient than drying out the river with cofferdams. The Olmsted Dam construction would have required building and taking down four of them.

One Down, 35 to Go

On Sept. 27, the super gantry crane lifted the second concrete shell, weighing about 3700 tons. After they place that second shell—using high-tech sonar and video-imaging equipment to see through the murky water to where they need to drive 2-foot-diameter piles to keep the shells in place—they will keep building the shells up and hauling them out in a sort of just-in-time manufacturing process. Workers can only build when the river is low enough for the catamaran barge to reach the bottom, seven months of a calendar year. The goal is to install six shells per year, and finish the dam by 2016.

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